Advantages or Disadvantages of AJAX
Reduce the server traffic in both side request. Also reducing the time consuming on both side response.
AJAX is much responsive, whole page(small amount of) data transfer at a time.
AJAX make asynchronous calls to a web server. This means client browsers are avoid waiting for all data arrive before start the rendering.
This is the biggest advantage. Form are common element in web page. Validation should be instant and properly, AJAX gives you all of that, and more.
No require to completely reload page again. AJAX is improve the speed and performance. Fetching data from database and storing data into database perform background without reloading page.
1. AJAX application would be a mistake because search engines would not be able to index an AJAX application.
2. Open Source: View source is allowed and anyone can view the code source written for AJAX.
3. ActiveX requests are enabled only in Internet Explorer and newer latest browser.
4 The last disadvantage, XMLHttpRequest object itself. For a security reason you can only use to access information from the web host that serves initial pages. If you need to fetching information from another server, it's is not possible with in the AJAX.